1. Field of the Invention
The present invention generally relates to late potential detection, and in particular to a system comprising an implantable medical device for detecting late potentials of a cardiac ventricle.
2. Description of the Prior Art
Cardiac arrhythmia, sometimes denoted dysrhythmia, encompasses a large heterogeneous group of medical conditions in which there is abnormal electrical activity in the heart of a patient. For instance, the heart may beat too fast or too slow, and may possibly beat regularly or irregularly. Arrhythmias may be benign or potentially life-threatening. Ventricular tachycardia (VT) is an example of the latter and involves fast heart rhythms that originate in one of the ventricles of the heart. This condition is a potentially life-threatening arrhythmia because it may lead to ventricular fibrillation (VF) and sudden death. Ventricular fibrillation involves a multitude of micro-reentry circuits and quivering with chaotic electrical impulses throughout the ventricle(s). Ventricular fibrillation is always a medical emergency and can lead to death within minutes if left untreated. The chaotic electrical impulses in the myocardium of the ventricle significantly reduce the effective blood pumping and may even cause a total stop of the pumping.
Today, more than 450 000 Americans die suddenly each year from sustained ventricular tachycardia or fibrillation. Overall, event rates in Europe are similar to those in the United States.
There is, thus, a great need for being able to detect ventricular tachycardia and/or fibrillation at an early stage in order to put in compensating therapy to stop the arrhythmic condition of the heart. One technique for predicting arrhythmic conditions, such as ventricular tachycardia and fibrillation, is based on the detection of ventricular late potentials (VLP).
Ventricular late potentials represent delayed conduction through a diseased myocardium and are due to the presence of electrical activity in the myocardium of the ventricle after the end of the QRS complex. These aberrant, asynchronous electrical impulses typically arise from viable isolated cardiac muscle bordering an infracted area and are potential substrates for ventricular tachyarrhythmias.
The traditional approach of finding such ventricular late potentials has been to use surface 12-lead electrocardiography (ECG) and so called signal averaged ECG. A patient to be investigated then has to visit a physician to record surface electrograms for multiple consecutive heart cycles. The recorded electrical activity of the heart during these multiple consecutive heart cycles are then signal averaged in a computerized analysis. The physician must then manually investigate the resulting signal averaged ECG in order to detect abnormalities corresponding to ventricular late potentials. Even with the signal averaged ECG it can be very hard to detect any ventricular late potentials, which put high demands on the investigating physician. Signal averaged ECG procedures are disclosed in the art, for instance in U.S. 2005/0234355 and U.S. Pat. No. 6,058,328.
The prior art solutions require the patient to visit the physician at the clinic in order to investigate whether the patient suffers from any ventricular late potentials, which of course is time and cost consuming for both the patient and the healthcare system. Additionally, there is a significant risk of missing patients suffering a risk of arrhythmias using the prior art solution as it may happen that a patient can suffer from ventricular late potentials that come and go. In such a case, there might be no ventricular late potentials detected during the visit at the clinic though the patient may still suffer from ventricular late potentials that occur at other time periods and therefore run a risk of arrhythmias.
There is therefore a need for an automatic solution allowing identification of late potentials of sufficient accuracy and that is not marred by the drawbacks of signal averaged ECGs.